As a technology for generating desired gaits of a moving robot, such as a bipedal moving robot, there has been known a technology in which an error of a floor reaction force moment about a desired ZMP or an error of an actual ZMP from the desired ZMP is observed and a gait is corrected to reduce the error, as disclosed in, for example, Japanese Patent No. 3443077 (patent document 1) or in “Realtime walking stabilization control of a biped humanoid robot—Verifying the validity of a walking control module in HRP—”/3P14/The 18th Annual Conference of the Robotics Society of Japan (non-patent document 1).
However, these technologies do not consider an error of a translational floor reaction force; therefore, if a gait is to be generated for a robot to walk on a road surface having a low friction coefficient or if a gait having a period during which a translational floor reaction force vertical component becomes zero or substantially zero, such as in running, is to be generated, it will be difficult to generate a gait that restrains the robot from slipping.
Thus, technologies disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-326173 (patent document 2) and PCT international publication WO/03/057427/A1 (patent document 3) have been proposed by the present applicant. According to the technologies disclosed in these patent documents 2 and 3, an instantaneous desired gait composed of an instantaneous value of a desired motion (instantaneous desired motion) of a robot and an instantaneous value of a desired floor reaction force (instantaneous desired floor reaction force) is sequentially created using a first dynamic model (simplified model), which represents a relationship between motions of the robot (the positions and postures of individual portions) and floor reaction forces, such that a dynamic balance condition (a condition, such as the one in that a translational force component of a floor reaction force takes a desired value or a floor reaction force moment about a certain point takes a desired value) on the first dynamic model is satisfied. Then, the instantaneous desired gait is input to a second dynamic model (full model) wherein a part of the instantaneous desired motion (desired body position/posture, a desired moment about a desired ZMP, or the like) is corrected so as to generate a final instantaneous desired gait in a time series manner.
According to the technology, using a model having high linearity as the first dynamic model (simplified model) makes it possible to efficiently and promptly create a gait that enables a robot to continue a stable motion, and using a model having relatively high dynamic accuracy as a second dynamic model (full model) makes it possible to bring the dynamic accuracy between a motion of a finally generated gait and a floor reaction force closer to the dynamics of an actual robot.
Meantime, according to the technologies disclosed in the aforesaid patent documents 2 and 3, the correction of an instantaneous desired motion (the correction of body position/posture) using the second dynamic model at arbitrary time t is made by using a past value of a moment about a desired ZMP (a correction amount of a moment about a desired ZMP) output from the second dynamic model. More specifically, according to the technologies disclosed in patent documents 2 and 3, a past value of a moment about a desired ZMP output from the second dynamic model is considered to indicate the dynamic error of an instantaneous value of a gait newly created using the first dynamic model and then the instantaneous value of a new gait is corrected on the basis of the past value of the moment. In other words, there is a temporal difference between the motion of a gait that has been finally corrected using the second dynamic model and a floor reaction force (the moment about a desired ZMP) that is referred to when making the correction.
However, the dynamic error of a gait created using the first dynamic model changes, depending on a gait motion pattern, so that the past value of the moment about the desired ZMP output from the second dynamic model does not necessarily indicate a dynamic error of an instantaneous value of a new gait created using the first dynamic model. Further, the second dynamic model has high nonlinearity, so that a motion of a gait created using it tends to diverge. Hence, according to the technologies disclosed in patent documents 2 and 3, it has been necessary to correct a desired ZMP trajectory or to generate a floor reaction force moment about a desired ZMP so as to restrain a desired motion trajectory of a robot from deviating from a motion trajectory of a gait created using the first dynamic model. And in this case, there have been occasions where a correction amount of a desired ZMP trajectory or a floor reaction force moment about a desired ZMP becomes relatively large, which has sometimes led to a difficulty in maintaining a large stability margin. Conversely, if the permissible range of a correction amount of a desired ZMP trajectory or a floor reaction force moment about a desired ZMP is set to be narrow in order to maintain a large stability margin, then the danger of the divergence of a gait has inconveniently increased.
The present invention has been made with a view toward the aforesaid background, and it is an object thereof to provide a gait producing device for a moving robot that is capable of efficiently generating a gait that permits prevention of a slippage of a robot and also capable of successfully securing dynamic accuracy between a motion of the gait and a floor reaction force while ensuring temporal coordination therebetween.